As a light source of a surface light source device of an edge-lit type with a hollow structure, there has been known a light source using a light-emitting diode (hereinafter, referred to as “LED”). In such a surface light source device, there is a case where a combination of an LED and a columnar or tubular light guide member may be used in order to control the distribution of light emitted from the LED (see, for example, PTL 1).
PTL 1 discloses a back light (surface light source device) having a reflection plate disposed on the bottom surface, a plurality of rod-like light sources disposed over the reflection plate, and a polarizing plate disposed over the plurality of rod-like light sources. The rod-like light source has a pipe body having a plurality of light collecting points over its outer peripheral surface, and light sources disposed on both ends of the pipe body.
In the back light set forth in PTL 1, light emitted from the light source moves forth inside the pipe body, and then is released from the light collecting part. Light released from the light collecting part toward the bottom surface is reflected by the reflection plate in the direction of the polarizing plate. On the other hand, light released from the light collecting part toward the top surface directly reaches the polarizing plate.